diff --git a/reactos/dll/win32/winmm/winmm.c b/reactos/dll/win32/winmm/winmm.c
index 325f0d5f5b3..c33fed12277 100644
--- a/reactos/dll/win32/winmm/winmm.c
+++ b/reactos/dll/win32/winmm/winmm.c
@@ -568,6 +568,9 @@ UINT WINAPI mixerGetLineInfoW(HMIXEROBJ hmix, LPMIXERLINEW lpmliW, DWORD fdwInfo
 
     TRACE("(%p, %p, %08lx)\n", hmix, lpmliW, fdwInfo);
 
+    if (lpmliW == NULL || lpmliW->cbStruct != sizeof(*lpmliW))
+	return MMSYSERR_INVALPARAM;
+	
     if ((uRet = MIXER_GetDev(hmix, fdwInfo, &lpwm)) != MMSYSERR_NOERROR)
 	return uRet;